Experimental quantum computing without entanglement

TL;DR

This paper demonstrates that quantum computational advantages can be achieved without entanglement by using quantum discord, challenging the traditional view that entanglement is essential for quantum speed-up.

Contribution

The study experimentally implements a DQC1 algorithm, showing non-classical correlations via quantum discord in the absence of entanglement, suggesting discord as a key resource.

Findings

No entanglement observed in the implemented algorithm

Non-classical correlations quantified by quantum discord are present

DQC1 model is resource-efficient and practically scalable

Abstract

Entanglement is widely believed to lie at the heart of the advantages offered by a quantum computer. This belief is supported by the discovery that a noiseless (pure) state quantum computer must generate a large amount of entanglement in order to offer any speed up over a classical computer. However, deterministic quantum computation with one pure qubit (DQC1), which employs noisy (mixed) states, is an efficient model that generates at most a marginal amount of entanglement. Although this model cannot implement any arbitrary algorithm it can efficiently solve a range of problems of significant importance to the scientific community. Here we experimentally implement a first-order case of a key DQC1 algorithm and explicitly characterise the non-classical correlations generated. Our results show that while there is no entanglement the algorithm does give rise to other non-classical correlations, which we quantify using the quantum discord - a stronger measure of non-classical correlations that includes entanglement as a subset. Our results suggest that discord could replace entanglement as a necessary resource for a quantum computational speed-up. Furthermore, DQC1 is far less resource intensive than universal quantum computing and our implementation in a scalable architecture highlights the model as a practical short-term goal.